Hello. I'm Richard Cornall.
I'm the Nuffield Professor of Clinical Medicine at the University of Oxford,
and I'm going to talk to you today about B-cell biology.
A good place to start is an overview of the function of B-cells,
which are called B-cells because they were discovered in
the bursa of Fabricius in poultry.
B-cells are characterised,
of course, by a B-cell receptor,
which doesn't itself signal but is associated with
Ig-alpha and -beta chains which contain immunoreceptor tyrosine-based activation motifs,
also known as ITAMs.
I'm not going to discuss the actual signaling mechanisms in detail here today.
The mode of B-cell activation is actually quite controversial,
at least in vitro activation is by
cross-linking and increasing the density of kinases relative to phosphatases.
But in vivo, most B-cells, it's now
appreciated, encounter antigen probably on the surface of other cells,
and how that operates at low density is not entirely known.
We look at the individual functions of B-cells.
The most well known is,
of course, antibody secretion,
and this arises through B-cells being activated and then differentiating into
plasma cells which secrete antibody
either on the short-term or over long-term in the bone marrow.
The second function of B-cells is to bind
antigen through the B-cell receptor and present them
on MHC class II receptors to activate the T-cell and obtain T-cell help.
Third function, which has been appreciated more recently is to transport antigen
within lymph nodes and the spleen particularly notably on complement receptors.
The fourth function of B-cells is to secrete cytokines.
In particular, some B-cells secrete IL-10,
and these cells are defined by some groups as being regulatory B-cells.
But unlike regulatory T-cells,
there's no transcription factor that has been
identified to define them as a unique subset.
These functions may be overlapping with other activatory functions of
B-cells and the plasticity of the B-cell subsets is not as yet clearly defined.